1. Field of the Invention
The present invention relates to a developer for a resist, and a resist pattern formation method using such a developer.
2. Description of the Related Art
In conventional production processes for semiconductor elements or liquid crystal elements, a lithography process is conducted to form a pattern on the substrate being processed. During this lithography process, a thin film of a photosensitive material known as a resist is applied evenly across the surface of the substrate to form a resist film (resist layer), and this film is then exposed through a mask pattern, and subsequently developed to form a resist pattern.
Resists are materials which display a change in solubility as a result of cross linking reactions or bond breaking which occur on irradiation with light or a variety of other beams, and perform two roles, namely, the formation of a real image of pattern information (exposure through to the development process), and as a mask for the processing of another layer (an etching process).
Resists include both positive resists and negative resists. During the development process, the exposed portions of a positive resist dissolve in the developer, whereas the unexposed portions remain undissolved. In contrast, in a negative resist, the unexposed portions dissolve in the developer, and the exposed portions remain.
The fineness of the pattern that can be formed is proportional to the wavelength of the light source used in the exposure. Accordingly, in order to further miniaturize resist patterns, the light sources used must be shifted to shorter wavelengths. As a result, in recent years there has been a shift away from the conventional i-line radiation (exposure wavelength 365 nm), and KrF excimer lasers (248 nm) are becoming more widely used. In addition, development of the next generation light sources, including ArF excimer lasers (193 nm) and F2 excimer lasers (157 nm) is also proceeding rapidly.
Resists for use with these excimer lasers are known as chemically amplified resists, and typically comprise a homogenous solution of a base resin and an acid generator dissolved in an organic solvent.
Chemically amplified resists utilize acid catalysis, and incorporate an acid generator which generates acid on exposure, and a base resin with a high reactivity to acid (and in the case of a negative resist, an additional cross linking agent).
The reaction of a chemically amplified resist is described using a positive resist as an example. First, when the positive resist is exposed, the acid generator becomes excited and emits a proton. Subsequently, by performing heat treatment by PEB (Post Exposure Baking), these protons attack the protective groups (acid dissociable, dissolution inhibiting groups) of the base resin, and these protective groups are eliminated, causing the base resin to become soluble in an alkali developer.
Conventionally, alkali aqueous solutions are widely used as developers for resists. However, if an alkali aqueous solution containing metal ions is used as a developer, then problems can occur in the characteristics of the semiconductor element or liquid crystal element, and as a result, developers containing an organic alkali such as tetramethylammonium hydroxide (TMAH) dissolved in water are typically used in preference to inorganic alkalis such as sodium (hydrogen) carbonate, potassium (hydrogen) carbonate or sodium hydroxide.
TMAH has considerable advantages in that it is cheap, and very reliable in terms of its effect on elements, although developers containing TMAH or the like do suffer from problems, such as reductions in resolution and film thinning, resulting from the developer penetrating into the unexposed portions of the resist.
In addition, in recent years, with the move towards even more finely detailed resist patterns, a resist developer capable of improving the resolution and shape of the resist pattern has been keenly sought.